SEGREGATION OF EU IMPLANTED AT THE MGO(100) SURFACE

The surface segregation of Eu implanted at the MgO(100) substrate has been investigated using time-of-flight coaxial impact-collision ion sc attering spectroscopy (TOF-CAICISS) and reflection high-energy electro n diffraction (RHEED). It is found that Ca impurities, which are inclu ded originally in the bulk of MgO in an amount of 210 ppm by weight, a re segregated to the surface after the implantation of 200 keV Eu+ ion s. Segregation of the implanted Eu occurs when the substrate is anneal ed at 1000 degrees C in ultrahigh vacuum (UHV; 5 x 10(-10) Torr). In t he process of Eu segregation, Eu is located at the substitutional posi tion of Mg, in addition to the interstitial position of the MgO lattic e. This indicates that there are two types of pathway for the segregat ion of Eu. At the last stage of Eu segregation, it is seen that Eu is concentrated at the outermost surface layer, protruding from the origi nal MgO plane by 0.3 Angstrom. (C) 1997 Elsevier Science B.V.